Matt Shakman just made his directorial debut on HBO's "Game of Thrones" with one of the series' greatest episodes yet. The 41-year-old director has previously worked on series such as "It's Always Sunny In Philadelphia," "Fargo," and "Mad Men," so diving into the new world of Westeros with this epic episode was a daunting task.

"I was filled with both excitement and terror as I realized what I was about to tackle," Shakman told INSIDER. "And then I went at it for the next six months."

We spoke with Shakman about the first step he took when piecing together the Lannister/Targaryen battle, how dragons are akin to napalm or atomic bombs, and why the Stark reunion was a delicate challenge.

Kim Renfro:
How much did you know about the two episodes you would be directing before you signed on with HBO?

Matt Shakman:
Nothing until I said yes and signed on the dotted line and signed all the NDAs [nondisclosure agreements] and double-verified my email. Then I was sent the scripts for the whole season, so I started reading at the beginning. I'm an avid fan, so it was a thrill to make my way through them.

I got to episode four, which was great with the reunion of the Starks. And then, I was just as surprised as everybody else when I got to the giant ambush at the end.

This was one of the biggest battles involving horses and CGI to date.
HBO

Renfro:
What was the first step in figuring out how to do this episode, since it's so different than the other directing work you normally do?

Shakman:
Yeah, it is different. I think that no one who hasn't directed "Game of Thrones" is really prepared to direct "Game of Thrones," because there's nothing else really like it out there. I mean luckily having traveled around and done lots of different things involving digital effects or stunts or special effects along the way, I felt like I sort of had the basic tools in my tool kit. It was just about sort of applying them to a much larger project than I'd ever done before and bringing them all to bear in the same sequence.

Jaime and Bronn were the centerpieces of the battle.
HBO

But before I got down into the minutia, I first wanted to figure out what the story of the battle was for me. There are a lot of perspectives and points of view in it, so I wanted to make sure I knew what I was prioritizing. The first thing I decided was that I wanted it to be mostly from Jaime and Bronn's point of view and I wanted to tell the story of what it was like to be on the ground and in the middle of a dragon attack and what it was like when war changes forever and a truly horrific weapon like napalm or an atom bomb is suddenly unleashed and what that does to the men on the ground.

Because we've seen dragon battles before and they're very exciting. You're with Daenerys as she kills the slavers in Meereen and that's all very heroic and you're rooting for her, but this is suddenly the first battle where you've got two opposing people who you're really rooting for and you like and you're not sure how you feel about them going up against each other, so I wanted to make sure we felt that humanity.

Drogon is capable of mass murder.
HBO

And then once I figured out thematically what I was doing, I started to plan out the logistics of it and the staging of the whole sequence [...] then we got ourselves in Spain and tried to deliver the actual goods.

Renfro:
What was the biggest challenge of this episode that wasn't related to the loot train battle?

Shakman:
I think handling the reunion of the Stark children. You wanted to bring a deft touch to something that people had been waiting years for. We all want to see them reunited, but they can never really be reunited, [because of this idea] that the people they are now are so different from the people that they were when they were separated.

So bringing Arya and Sansa together is great. They've become much stronger versions of the people they were before. Arya was always a scrapper and a fighter and Sansa was always more refined and interested in being queen. Now Sansa is the Lady of Winterfell and a strong political operative and Arya has become this amazing assassin and fighter. For them to see what the other has become I think was quite exciting but also needed to be handled carefully.

Sansa (Sophie Turner) and Arya (Maisie Williams) haven't seen each other since the first season.
Helen Sloan/HBO

One of my other favorite scenes in the episode was Arya and Brienne and their practice session, which Sansa oversees and really becomes the evidence for Sansa of how much Arya has changed.

Renfro:
Right because we go through the stages with Sansa thinking that Arya is joking about her list, and then learning through Bran that it's not a joke, and then she finally sees Arya in action. So is that the reaction we were seeing from Sansa, it was just, "Oh wow, she really is deadly"?

Shakman:
Exactly, yeah. I think you described it perfectly — there's stages to it. [Sansa] thinks [Arya's] kidding in the crypts and then she gets to the tree and Bran confirms this idea that she has a list, but doesn't really know what she's done with this list completely, although Arya does suggest she's done some deadly things.

And then Arya's out there with Brienne — who is Sansa's protector, her bodyguard, the person she's relied on to keep her safe in this dangerous world — and all of the sudden her tiny little sister is fighting Brienne to a draw at the end with a sword and knife to each other's throats. And it causes her to quickly redefine her relationship with Arya and to wonder who exactly her little sister has become.

Arya and Brienne (Gwendoline Christie) were a great match.
Helen Sloan/HBO

Renfro:
And what was it like in the off-set moments with Maisie Williams and Sophie Turner, because we know how close they are as friends and this was the first time they were getting to work together in years.

Shakman:
It's fun, some of the first scenes that I shot and some of the first scenes they shot this season were scenes together, and they were giggling and having kind of an awkward time because they're very, very good friends and they felt awkward acting with each other.

They felt that they weren't up to it. They were worried the other one would think they were bad, but they're both amazing actors so they quickly settled into a rhythm.

Williams and Turner are BFFs in real life.
Helen Sloan/HBO

The scenes together are fantastic but whenever we would cut they would just giggle or even sometimes when we didn't cut they'd be giggling through the scene, but they eventually found their way through it. It's great. I think the warmth that they have off screen is certainly an asset for what they have to go through on screen as well.

Renfro:
Back to the big battle, a lot of book readers and people familiar with George R.R. Martin's lore know about the "Field of Fire," another historic battle between Targaryens and Lannisters. Was that on the table as a starting point for building what this new version of that would look like?

Shakman:
No, I've seen that a little bit online and people referring to this as "Field of Fire 2.0." And as a great fan of the series, I've only read the first book. I'm not deeply steeped in the lore, so my lore is pretty much restricted to the television show.

Jaime's fate was left uncertain at the episode's end, though we think he'll survive.
Macall B. Polay/HBO

So no we didn't talk about that much. We talked mostly about the point of views and references. I looked at "Apocalypse Now," which has a tremendous battle between guys in a helicopter and villagers down below and shifts perspectives and it's very much about the horrors of war. I looked at things like that for inspiration. But no, I did not go too deep into George Martin.

Renfro:
Last small thing — I think since people had trouble picking sides in this battle, we all just wound up feeling really bad for the horses. Is there anything you can say to those fans who were left feeling sad about all the horse maiming?

So many brutal horse deaths!
HBO

Shakman:
Those horses are all fake. They're all well fed and well-loved and nothing happened to any of them in the making of it. But certainly the horses as characters suffered a pretty rough go in the sequence and that was a pretty big part of it. I watched the show with a friend of mine last night who's a huge horse lover and she was just gasping and freaking out at the leg getting cut off and horses on fire and all that sort of stuff. You know, the dragon doesn't spare the horses either. Humans and horses alike get burned unfortunately. It's tough out there.